Flame detecting apparatus



A 1951 L. J. DAHLINE 2,564,596

FLAME DETECTING APPARATUS Origjmal Filed Dec. 30, 1946 w n E i w v j j w w in w. J fi n H. u

(Ittorneg Patented Aug. 14, 1951 FLAME DETECTING APPARATUS Lawrence J. Dahline, "Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Original application December 30, 1946, Serial No. 719,291. Divided and this application December 26, 1947, Serial No. 793,820

Claims. 1

The present invention is a divisional application of my copending application for Fire Detecting Apparatus, Serial No. 719,291, filed December 30, 1946, now U. S. Patent 2,478,373.

The present invention is concerned with a type of flame detection system employing a rectifying flame sensitive impedance with electronic devices that will respond to any rectifying action that takes place when a flame is present at the flame detecting apparatus and more particularly such apparatus of the type depending for its operation upon current flow between two spaced electrodes when bridged by a flame.

It has been proposed in early types of flame detection systems to utilize the rectifying properties of a flame in one way or another to control the bias on some type of electron discharge device. Connected in circuit with the discharge device is some indicating device which upon the presence of flame will indicate that fact by an alarm. These early detection systems have had many'characteristics which have inadvertently complicated the system. For example, many of these systems react sporadicall to various flame conditions and to shorting impedances in the flame detector elements which give an indication which cannot be relied upon.

In providing an ideal flame detection system, the system must employ some detecting means which is not sensitive to light so the detection apparatus may be placed in any position. It is also necessary to have a system that will distinguish between a continued flame and a momentary flash of flame as might occur upon a back fire of an internal combustion engine. The system must e able to distinguish between a flame condition and a condition of equipment failure, such as a short in the detecting elements or where the detecting elements are bridged by a flame like impedance. Another feature needed is some method of preventin high current arcs at flame electrodes especially when the electrodes are located in an area where much combustionable fuel is present as at the carburetor.

It is therefore an object of the present invention to provide an improved flame indicating system of the type that will be able to distinguish between a condition of short circuit and one of flame regardless of how that short circuit is caused.

A further object of the present invention is to provide protection from a high current are in the event of a short circuit at the flame electrodes.

A still further object of the present invention is to provide a system that will respond quickly to any continued flame condition but will not respond to a flash of flame as is caused by a backfire.

Still another object of the present invention is to provide a flame indicating apparatus which utilizes an electron discharge device whose current flow is an indication of the presence or absence of flame and having an electrical filter network on its input terminals to prevent a momentary appearance of flame from actuating the discharge device.

A still further object of the present invention is to provide an indication of how the system is functioning upon the turning on of the system.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims, and drawing, in which:

The single figure is a schematic view of my fire detecting apparatus employed in connection with an airplane engine.

The numeral [0 is employed to designate a portion of a nacelle unit of an airplane engine. Included within this nacelle is an engine compartment H and the accessory compartment l2. The engine compartment I l is generally enclosed by a cowl 13 shown by dotted lines on the diagram. Numeral I4 designates the cylinders of the engine. The exhaust system of the engine includes an exhaust pipe 15 and a common exhaust manifold 16. The numeral l'l designates the forward nose portion of the engine through which the drive shaft, not shown, extends and on which is fastened the propeller hub [8. Extending from the propeller hub l8 are propeller blades I 9. Located between the engine compartment II and the accessory compartment I2 is a fire wall 20. An oil cooler shroud 21 and a carburetor intake 22 lead touan oil cooler and a carburetor respectively located within the accessory compartment I2.

Power is supplied to the apparatus through lines 30 and 3|. In a line 34 connecting line 3| and terminal 35 of a housing 40 is located a switch 32 and an associated contact 33. Gonductor 36 connects line 30 to terminal 31 of housing 43. Grounding of the system is done by ground 38 connected to conductor 36. Connected to terminals 35 and 31 of housing 40 is a primary winding 42 of transformer 4|. A high voltage winding 43 and a low voltage winding 44 comprise the secondary windings of transformer 4|. The low voltage winding 44 supplies filament voltage through conductors 45 and 46 to filaments 59 associated with triode 5| and triode 52 located withand switch arm 12 biased normally to a closed position. Energizing of relay winding 54 causes the armature 13 to move the switch arm 12 from the contact I l. A by-pass condenser 15 is in parallel with the relay winding 14m smooth out the pulisating current flowing through the plate cir- C111 The operating voltage for the triodes 5i and 52 is obtained from that section of the transformer winding 43 located above center tap 16. The control grids 54 and 5'! are connected in the other half of the high voltage winding 43 that is located below the center tap T6. In circuit with this connection is a chargeable condenser 89 and a filter comprising a resistor 82 and a condenser 83. Biasing resistors 84 and 89 are associated with control grids 54 and 51 respectively and act as load resistors for condenser 83.

A current limiting resistor 99 is in the flame detector circuit and is connected to a flame electrode 96 through terminal 94 of housing 49. The return circuit provided'for the flame detection system is by way of connection '95 and terminal .93 of housing 40 to the ground conductor 11. As-

sociated with the flame electrode 95 are high voltage insulators 91.

Within a housing H9 is located an indicating lamp I. An auxiliary power supply I29 is provided for the indicating lamp I I in the event of a power failure. A switch l2l and contact I22 are'used in the auxiliary power supply circuit.

While the various elements of the system described so far may have a wide range of values, in one particular embodiment of the invention it was found desirable to employ a transformer having a high voltage secondary winding with 300 volts available on both sides of the center tap. In the same embodiment a 7N7 type tube was employed. The condenser 88 was .001 microfarad while the condenser 83 was .02 microfarad. The by-pass condenser 15 had a value of .2 microfarad The grid biasing resistors 84 and 89 were each 30- megohms while the filter resistor 82 was 3 megohms. The current limiting resistor 99 had a value of 5 megohms. It is to be understood, as noted above, that these values are purely illustrative of those employed in one embodiment of the invention and that the invention is not in any way limited to the use of elements of these particular values.

Operation The apparatus is shown in the completely deenergized position with the switch arms of the relays in the position as shown on the diagram and the indicating lamp not energized. Closing the switch blade 32 energizes transformer 4| and thusly by way of transformer 44, and conductors 45 and 46 the filaments 59 will begin to heat up. Closure of the switch l2l will allow completion of a circuit for the storage battery l29 through switch l2l, contact I22, conductor H9, terminal H1, conductor H4, indicating lamp HI, conductor H5, terminal H8, terminal I99, contact H, switch arm 12, conductor 18, conductor 11, and ground connection 38; This last circuit will remain operative until such time as the filaments 59 have heated the cathodes 55 and 58 to the 4 current emissive point, in a manner to be described. Energizing the primary 42 of the transformer 4| will also energize the high voltage secondary winding 48. As soon as cathode 55 has been heated tov the electron emissive point it is possible to establish a current path from the upper terminal of transformer winding 43, through conductor 41, relay winding 14, conductor 81, plate 53, cathode 55, conductor ll, center tap it back to the winding 45. A similar cir cult can be established for the triode 52 when its cathode 58 becomes electron emissive. A conductive path may be established from the upper terminal of transformer winding 43, through conductor 41, relay winding 14, conductor Bl, con

ductor 88, plate 56, cathode 58, grounded conductor TI, center tap it back to the winding 43. The control grid 54 is connected to a point in the power supply that is considerably more negative than the cathode, however, since the connection is by way of a voltage dividernetworl; including condenser 89, resistor 82 and condenser 83 to the lower portion of winding 43 itis, possible for the control grid to be only slightly negative with respect to the cathode 55. Without the addition'of anyfurther voltage on the control grid 54 it is possible for the triode 5l to conduct during the positive half cycles of the alternating power source. By the same token, it is posible for triode 52 to conduct because there is a direct connection between control grid 54 and control grid51 by way of conductor 85.x e r As soon'as tubes 5! and 52 are in a conducting state a plate current from the tubes will flow through relay winding 14 and will cause the armature 13 to move the switch arm 12 fromthe contact H and open the circuit to the lamp, 1 IL With the extinguishing of the lamp Ill the ob server is assured of the proper operation of the alternating power sourceof the'detection apparatus as well as the system in general. During the negative half cycles of the alternating power source the control grids 54 and 5? willtendto go positivewith respect to their respective cathodes 55 and 58, such that there will'be a grid current flow. This grid current flow will tend to charge the condenser such that the right hand-side will be negative and the left hand side positive. Since the positive voltage applied to the grids, .54 and 41-, is very small because of the effective volte' age divided network comprising condenser 38-,re sistor 82 and condenser 83 in the circuit between the lower half of the winding 43 and the grids and cathodes of the tubes 5! and 52 it canbe seen that the grid current'flowing will be'very small and the resultant'charge in condenser 88 will be negligible. The little charge that is accumulated on condenser'BU will have littleeffect on the conductivity of the tubes and any resultant decrease in plate current how will not deenergize the relay winding 14. i

' Should a flame bridge the'gga between the electrode 96 and the fire wall 29a resultant conductive path would allow the'completion ofjan alternating current path starting from the lower terminal of the high voltage secondary winding 43 through conductor '79, condenser 80, resistor 90, conductor 92, terminal 94, electrode 96, the flame conducting path, fire wall 20, connector 95, terminal 98, conductor 9!, conductor 11 and center tap 16 of the winding 43. Because of the alternating current supplied to the circuit and the fact that the flame has rectifying properties it is possible to build upa charge on condenser 80 uch. th t th onden er 8 will. assume a char accuse that isnegative on the right side and positive on the left side.

As the circuit impedances of the flame rectifler, including the impedance of the flame gap, are lower than the grid-cathode rectifier circuit impedances, with the same voltage applied, a larger current will flow in the flame rectifier and will therefore charge condenser 80 an appreciable amount.

With the right side of the condenser 80 connected by way of conductor BI, and resistor 82 to the grid 54, and the left side of condenser 80 connected by conductor 19, lower half of secondary winding 43, center tap l6, and ground conductor TI to the cathode 55, it may be seen that any voltage charge on condenser 80 will have a biasing effect on the tube As tube 52 is normally connected in parallel with tube 5| the biasing effect will be felt on tube 52. The voltage charge built up on condenser 80 due to a flame is sufiicient to bias the tubes 5| and 52 and decrease the plate current flow of these tubes. With the decreased plate current flow it is impossible to maintain relay in an energized position which will result in the armature 13 allowing switch arm 12 to close with contact H and complete a circuit to lamp H to indicate,

The resistor 82 and condenser 83 that form a filter network on the input to the grids of the triodes 5| and 52 act in a time delay sense to prevent the grids from being cut ofi' immediately. This is readily apparent when one considers that the filter network is in parallel with condenser 80 and the lower section of the winding 43. Since the condenser 83 tries to assume the same potential as condenser 8!! there will be a current flow through resistor 82 which tends to slow down the charging of the condenser 83. This time delay as controlled by the RC time constant of the filter network is chosen so as to make the system insensitive to a flash of flame or a back fire.

With the relatively high voltage applied to the flame gap circuit by way of the lower half of the high voltage winding 43 it is apparent that a short or a break down of the insulators 9'! would allow a high current are to be present were it not for the current limiting resistor 90. Were such an arc present it would obviously ignite any combustible fuels present in the area. The current limiting resistor 90 also functions to protect any personnel who might be working in the vicinity of the flame electrode 96 since a lethal amount of current would not flow through a resistor of proper size.

In the event of a short circuit between the electrode 96 and the fire wall 20, the indicating system would not indicate a flame condition because the circuit established by the short circuit would tend to connect the right side of limiting resistor 90 to the cathode connection of tubes 5| and 52 through conductor 92, terminal 94, electrode 96, the short circuit, fire wall 20, terminal 95, terminal 93, and conductor 9|. The limiting resistor 90 is now in parallel relationship with the filter network comprising resistor 82 and condenser 83 and the biasing resistor 84 so that the alternating voltage on the control grids of tubes 5| and 52 will be even less negative than it was prior to the short. Obviously the conductivity of tubes 5| and 52 will not have been decreased and therefore the relay 10 remains in an energized position and will not allow the indicating light circuits to be closed.

Were the flame electrode 96 and the-fire wall 20 bridged by a flame-like impedance no rectification would take place and therefore no charge would be accumulated on condenser which would mean that the conductivity of the triodes 5| and 52 would not be altered to allow deenergization of the relay 10. With a flame bridging the flame gap in addition to a "flamelike impedance there will be sufficient rectification from the flame to charge condenser 80 an appreciable amount and ultimately deenergize relay 10.

Should a break occur in the electrode 96, the circuit would remain operative because there are two return paths to the terminal 94 since the electrode 96 is a complete circle.

While I have disclosed my fire detection system in connection with an airplane engine and while it is particularly suitable for such an application, it is to be understood that it could be employed in any condition where fire detection or indication is deemed of importance. In general, while I have disclosed a specific embodiment in my invention, it is to be understood that this is for purposes of illustration and that my invention is to be limited solely by the scope of the appended claims.

I claim:

1. In combination; an electron discharge device having an anode, cathode, and grid; a source of power having a plurality of points for connection; means for connecting said cathode to a first point on said source and said anode to a second point on said source; a condenser; a filter network; current rectifying flame responsive means; means connecting said condenser between a first terminal of said flame responsive means and a point on said source and connecting a second terminal of said flame responsive means directly to said first point on said source so that said condenser will be charged on the presence of a flame; means connecting said flame responsive means in parallel with said filter; and means connecting said filter in parallel with the grid-cathode path of said discharge device so that the charging of said condenser will affect the current flowing through said discharge device.

2. In combination, a transformer having a secondary with two end terminals and a tap, an electron discharge having an anode, cathode, and control electrode, a condenser, means connecting said condenser between said control electrode and one of said end terminals, means connecting said cathode to said tap, a current responsive means, means connecting said current responsive means between said anode and the other end terminal of said second so that current will normally flow through said discharge device and maintain said current responsive means in an energized position, a pair of terminals arranged for connection to a current rectifying flame responsive means, and means connecting said terminals between said cathode and the control electrode side of said condenser so that when said terminals are connected to the flame responsive means in a predetermined manner said condenser will be charged and will cause a decrease in the current flowing through" said discharge device to cause said current responsive means to assume a deenergized position.

3. In combination; a power transformer having a plurality of points for connection; an electron discharge device having an anode, cathode, and grid; means connecting said anode to a first point on said transformer; means connecting said cathode to a second point on said transformer; a two terminal condenser; means'connecting one terminal of said condenser to a point on said source; a current rectifying flame responsive means having two terminals; means connecting one terminal of said flame responsive means to the other terminal of said condenser and the other terminal of said flame responsive means to said second point on said transformer so that said flame responsive means will be eflective to charge said condenser on the presence of a flame; a filter network having input and output terminals; means connecting one of said input terminals directly to said other terminal of said condenser and the other of said input terminals to the other terminal of said flame responsive means so that said input terminals are in parallel with said flame responsive means; and means connecting the output terminals of said filter in parallel with the grid-cathode path of thedischarge device:

4. In combination; an electron discharge device having an anode, cathode and control element; a source of power having a plurality of points for connection; means connecting said anode to a first pointon said source; means connecting said cathode to a second point on said source; a condenser; means connecting said control element to third point on said source through said condenser; and a current rectifying flame responsive means connected directly through non-reactive connections between said cathode and the control electrode side of said condenser.

5. In combinationyan electron discharge device having an anode, cathode and grid; a source of power having a plurality of points for connection; means connecting said cathode to a first point on said source and said anode to a second point on said source; a condenser; a filter network; a pair of terminals which are arranged for connection to a current rectifying flame responsive means; means connecting said condenser in series with said terminals to said source so that when a flame responsive means is connected to said terminals, said condenser will be charged on the presence of a flame; means connecting said terminals directly through nonreactive connections in parallel with said filter; and'means connecting said filter in parallel with the grid-cathode path of said discharge device so that the charging of said condenser will effect the current flowing through said discharge device.

LAWRENCE J. DAI-ILINE.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,410,524 Richardson et a1 Nov. 5, 1946 Beam et a1. July 10, 1948 

